linux-kernel - Re: [Regression] Commit 02c24a82187d5a628c68edfe71ae60dc135cd178 breaks s2disk

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Message-Id: <201108020217.48952.rjw@sisk.pl>
Date:	Tue, 2 Aug 2011 02:17:48 +0200
From:	"Rafael J. Wysocki" <rjw@...k.pl>
To:	Josef Bacik <josef@...hat.com>
Cc:	LKML <linux-kernel@...r.kernel.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Linux PM mailing list <linux-pm@...ts.linux-foundation.org>,
	Al Viro <viro@...iv.linux.org.uk>, Jan Kara <jack@...e.cz>
Subject: Re: [Regression] Commit 02c24a82187d5a628c68edfe71ae60dc135cd178 breaks s2disk

On Tuesday, August 02, 2011, Rafael J. Wysocki wrote:
> Hi,
> 
> Unfortunately s2disk (which is a user space tool for saving hibernate images)
> doesn't work any more after your commit 02c24a82187d5a628c68edfe71ae60dc135cd178
> (fs: push i_mutex and filemap_write_and_wait down into ->fsync() handlers).
> The symptom is that the s2disk's resume counterpart cannot find the image in
> the device even though s2disk considers it as successfully saved.
> 
> What happens is that s2disk opens a block device (disk partition to be precise)
> directly and writes to it eventually calling fsync().  My interpretation of the
> failure is that before commit 02c24a82187d5a628c68ed, when s2disk called fsync()
> the VFS layer would run filemap_write_and_wait_range() that in turn would cause
> the data to go to the disk, but after that commit this doesn't happen any more.
> 
> If I'm right, then not only s2disk, but any process writing directly to a block
> device will have a problem with fsync().

Well, I'm not sure if the patch below is the right fix, but it evidently makes
s2disk work for me again.

Thanks,
Rafael

---
 fs/block_dev.c |    4 ++++
 1 file changed, 4 insertions(+)

Index: linux-2.6/fs/block_dev.c
===================================================================
--- linux-2.6.orig/fs/block_dev.c
+++ linux-2.6/fs/block_dev.c
@@ -387,6 +387,10 @@ int blkdev_fsync(struct file *filp, loff
 	struct inode *bd_inode = filp->f_mapping->host;
 	struct block_device *bdev = I_BDEV(bd_inode);
 	int error;
+	
+	error = filemap_write_and_wait_range(filp->f_mapping, start, end);
+	if (error)
+		return error;
 
 	/*
 	 * There is no need to serialise calls to blkdev_issue_flush with
--
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